Method for functionalising carbohydrates

ABSTRACT

The invention relates to a method for functionalising carbohydrates, that comprises at least one step during which the carbohydrates react with an oxidizing agent in the presence of copper-phenanthroline complex. The invention more particularly relates to a method for functionalising cellulose fibers for the paper industry.

The invention relates to a method for functionalising carbohydrates. It relates in particular to a method for functionalising cellulose fibers for the paper industry.

Functionalisation consists of the creation of carbonyl and in particular carboxyl functions, produced by oxidation of the alcohol functions naturally present in carbohydrates, such as for example cellulose paper pulp fibers or starches.

Document WO 92/18542 describes the oxidation of carbohydrates in an alkaline aqueous medium using oxygen gas in the presence of a metal ion selected from group VIII of the Periodic Table, and a substance acting as a ligand of the metal ion. This document teaches that the metal ion is preferably introduced into the alkaline medium in the form of a soluble salt. It further teaches that the ligand is preferably a polydentate amine.

Document U.S. Pat. No. 6,136,041 discloses the use of an additive to activate bleaching solutions for lignocellulosic fibers in oxidizing conditions. This document teaches that the additive may be selected from phenanthrolines and polypyridyls.

Document WO 03/080925 describes a delignification and prebleaching step in which the oxygen is used in combination with hydrogen peroxide in the presence of a phenanthroline-copper complex. The chemical paper pulp delignification and bleaching method consists in subjecting the pulps, after digestion, to several steps of delignifying and/or bleaching treatment. The first steps essentially consist in completing the delignification resulting from the digestion and the subsequent steps of bleaching steps.

In general, the phase of completion of delignification after digestion (also called prebleaching) consists of one to two delignification steps with reagents, such as for example oxygen (stage O) or oxygen in combination with hydrogen peroxide (stage Op), chlorine dioxide (stage D) and/or ozone (stage Z). On completion of the delignification treatment steps, the paper pulp may be subjected to treatment with alkaline reagents, such as for example caustic soda, in order to solubilize and extract the lignin attacked (alkaline extraction stage denoted by E). This treatment can be carried out in combination with oxygen (stage Eo) or in combination with hydrogen peroxide (stage Ep) or in combination with oxygen and hydrogen peroxide (stage Eop). This treatment can also be inserted between the delignifying treatment steps.

Finally, the bleaching step or steps consist in subjecting the delignified and prebleached pulp to treatment by bleaching agents, such as for example chlorine dioxide or hydrogen peroxide. In general, the actual bleaching concerns pulps having a Kappa number ≦6 and an ISO whiteness 60% (that is obtained after delignification and prebleaching). The Kappa number and the whiteness are measured respectively according to the standards ISO 302 and ISO 2470.

The applicant has now developed a method for functionalising carbohydrates, including paper pulps, cellulose and polysaccharides, including starch.

This method comprises at least one step during which the carbohydrates react with an oxidizing agent in the presence of a copper-phenanthroline complex.

The copper-phenanthroline complex may be formed from a copper salt and a phenanthroline ligand. The phenanthroline concentration is preferably between 0.001 and 1% and advantageously between 0.01 and 0.1% by weight of the material to be functionalised.

The cooper concentration is preferably between 0.0001 and 0.030% (or 1 and 300 ppm) and advantageously between 0.0001 and 0.015% (or 1 and 150 ppm) by weight of the material to be functionalised.

The oxidant concentration is preferably between 1 and 20% and advantageously between 2 and 10% by weight of the material to be functionalised.

As oxidizing agent, mention can be made in particular of peroxides, in particular hydrogen peroxide, peracids, in particular peracetic acid and performic acid, oxygen, ozone, chlorine, chlorine dioxide and sodium hypochlorite. Hydrogen peroxide is advantageously selected as the oxidant.

The phenanthroline is preferably selected from 1,10-phenanthroline, 4,7-phenanthroline and 1,7-phenanthroline; 1,10-phenanthroline is particularly preferred.

This method is suitable for functionalising cellulose and in particular for functionalising cellulose fibers of paper pulp.

According to a first alternative of the invention, the method comprises at least one step of delignification of the lignocellulosic material followed by at least one bleaching step during which the delignified cellulosic material is subjected to a treatment with an oxidizing agent in the presence of a copper-phenanthroline complex.

According to a second alternative of the invention, the method comprises at least one step of delignification of the lignocellulosic material, at least one alkaline extraction stage, at least one bleaching step and at least one treatment with oxidizing agent in the presence of a copper-phenanthroline complex, and the latter can be carried out during the alkaline extraction stage and/or the bleaching step.

Regardless of the alternative, the oxidizing agent treatment in the presence of a copper-phenanthroline complex is preferably carried out on pulp having a Kappa number ≦6 and an ISO brightness ≧60%, advantageously on pulp having a Kappa number ≦2.5 and an ISO whiteness ≧75% and advantageously preferred on pulp having a Kappa number ≦2 and an ISO whiteness ≧80%.

This treatment can be advantageously carried out in the final bleaching step or after the final bleaching step.

The reagents for the delignification step may be oxygen (stage O) or oxygen in combination with hydrogen peroxide (stage Op), chlorine dioxide (stage D) and/or ozone (stage Z).

The bleaching step can be carried out in the presence of chlorine dioxide and/or hydrogen peroxide.

The temperature of the treatment using oxidizing agent in the presence of a copper-phenanthroline complex is preferably lower than 85° C. and advantageously between 35 and 65° C.

The treatment time depends on the temperature selected, and is preferably shorter than 1 hour.

The consistency of the pulp during the treatment is preferably between 5 and 20% by weight and the reaction medium is preferably aqueous. The pH of the reaction medium is advantageously between 9 and 12.

The present invention is suitable for any type of paper pulp (mechanical, chemical, recycled pulp), preferably chemical paper pulp.

Chemical paper pulps or chemical pulps are those obtained by digestion of lignocellulosic materials in particular of wood. Among chemical pulps, a distinction is made between kraft or sulfate pulps, sulfite or bisulfite pulps, semi-chemical or neutral sulfite pulps, pulps after digestion with a solvent like those obtained by the Organosolv processes (Oilman's Encyclopedia of Industrial Chemistry, 5^(th) Edition, vol. A, 18, 1991, pages 568-569), sulfite-anthraquinone pulps.

All types of wood are suitable: coniferous woods such as the various species of pines and firs, deciduous woods such as for example birch, poplar, beech and eucalyptus.

The pulps thus functionalised can then be crosslinked to increase the strength of the desired end product.

The functionalisation method according to the present invention has the advantage of being easily incorporated in a conventional paper pulp treatment line and serves to avoid the use of costly and ineffective additives.

EXPERIMENTAL PART

The pulps subjected to the treatment with oxidizing agent in the presence of copper-phenanthroline complex had a Kappa number <1 and an ISO brightness >85%. These previously delignified and bleached pulps were of industrial origin:

-   -   Bleached cotton linters pulp (example 1), consisting nearly         exclusively of pure cellulose and containing very little         hemicellulose (<0.5%)     -   Bleached resinous kraft pulp (examples 2, 4 and 5) (mixed         conifers)     -   Bleached deciduous kraft pulp (examples 3 and 6) (mixed         hardwoods).

EXAMPLES 1 TO 3

The oxidizing agent used was hydrogen peroxide and the quantity employed was 6% by weight of the pulp to be treated. The quantity of copper-phenanthroline complex employed was 0.1% by weight of the pulp to be treated. The consistency of the pulp was 6% by weight and 2% by weight of caustic soda was added to the pulp. The treatment temperature was 45° C. and the time was 20 minutes.

The following procedure was applied: the pulp was dispersed in water and then placed in a plastic bag. The reagents were then introduced and mixed with the pulp in the following order: catalyst (Cu(Phen)₂ ²⁺ complex), caustic soda solution, hydrogen peroxide solution, so that the functionalisation stage took place at the desired consistency. The bag was then sealed and immersed in a water bath at the temperature and for the time selected.

The carboxyl content measured before and after functionalisation under the conditions described above is given in Table 1. This carboxyl content was measured by the methylene blue method (Tappi standard T 237, Wilson W. K., Mandel, J. “Determination of Carboxyl in Cellulose”, Tappi 44 (2), 131 (1961)).

TABLE 1 Results of functionalisation tests on three industrial pulps Example 1 Example 2 Example 3 Initial carboxyl 8 8 12 content (meq/100 g) Final carboxyl 25 28 27 content (meq/100 g)

EXAMPLE 4

The same procedure was followed as in Example 3, except that the treatment time was 50 minutes. The final carboxyl content obtained was 45 meq/100 g.

EXAMPLES 5-6 Crosslinking of Functionalised Pulps

After the functionalisation treatment, the pulps were crosslinked by heat treatment at 120° C. in the presence of sodium dihydrogenophospate. Example 5 relates to the crosslinking of the pulp obtained in example 2, where example 6 concerns the crosslinking of the pulp obtained in example 3. Table 2 gives the variations in the properties of the pulps obtained after functionalisation+crosslinking. These variations are given in % of the value obtained in the absence of functionalisation.

TABLE 2 Variation in mechanical properties of crosslinked pulps after functionalisation treatment Example 5 Example 6 Bulk −0.5%  −5.6%  Stiffness factor +43% +72% Breaking length +74% +53% Elongation index +75% +57% Tear factor +495%  +157%  Burst factor +190%  +157%  

1. A method for functionalising carbohydrates, including paper pulps, cellulose and polysaccharides, including starch, comprising reacting carbohydrates with an oxidizing agent in the presence of a copper-phenanthroline complex.
 2. A method for functionalising cellulosic fibers of paper pulps characterized in that it comprises delignifying lignocellulosic material to form cellulosic material followed by bleaching the cellulosic material with an oxidizing agent in the presence of a copper-phenanthroline complex.
 3. A method for functionalising cellulosic fibers of paper pulps characterized in that it comprises the steps of: delignifying lignocellulosic material to form cellulosic material, (b) treating the cellulosic material with alkaline to extract lignin, (c) bleaching the lignin with an oxidizing agent in the presence of a copper-phenanthroline complex.
 4. The method as claimed in claim 2, characterized in that the bleaching is carried out on cellulosic material having a Kappa number ≦6 and an ISO brightness ≧60%.
 5. The method as claimed in claim 1, characterized in that the oxidizing agent is hydrogen peroxide.
 6. The method as claimed in claim 1, characterized in that the temperature is lower than 85° C.
 7. The method as claimed in any one of claims 2 to 6, characterized in that the reagent(s) for the delignification step is (are) oxygen (stage O) or oxygen in combination with hydrogen peroxide (stage Op), chlorine dioxide (stage D) and/or ozone (stage Z).
 8. The method as claimed in claim 2, characterized in that the bleaching is via chlorine dioxide and/or hydrogen peroxide.
 9. The method as claimed in claim 2, characterized in that the paper pulp is of the chemical type.
 10. The method as claimed in claim 2, further comprising crosslinking said cellulosic materials after bleaching.
 11. The method as claimed in claim 3, characterized in that the bleaching is carried out on cellulosic material having a Kappa number ≦6 and an ISO brightness ≧60%.
 12. The method as claimed in claim 2, characterized in that the oxidizing agent is hydrogen peroxide.
 13. The method as claimed in claim 3, characterized in that the oxidizing agent is hydrogen peroxide.
 14. The method as claimed in claim 1, characterized in that the temperature is lower than 85° C.
 15. The method as claimed in claim 1, characterized in that the temperature between 35 and 65° C.
 16. The method as claimed in claim 2, characterized in that the temperature is lower than 85° C.
 17. The method as claimed in claim 2, characterized in that the temperature is between 35 and 65° C.
 18. The method as claimed claim 3, characterized in that the treatment temperature is lower than 85° C.
 19. The method as claimed in claim 3, characterized in that the treatment temperature is between 35 and 65° C.
 20. The method as claimed claim 3, characterized in that the bleaching is via chlorine dioxide and/or hydrogen peroxide.
 21. The method as claimed in claim 3, characterized in that the paper pulp is of the chemical type.
 22. The method as claimed claim 3, further comprising crosslinking said lignin after bleaching. 